Conventionally, in 3GPP (3rd Generation Partnership Project), the W-CDMA system has been standardized as a 3rd-generation cellular mobile communication system, and the service of the system has been started sequentially. Further, HSDPA (High-Speed Downlink Packet Access) with the communication speed further increased has been standardized, and its service has been about to start.
Meanwhile, evolution of 3rd-generation radio access (Evolved Universal Terrestrial Radio Access: hereinafter referred to as EUTRA) has been studied in 3GPP. The OFDM (Orthogonal Frequency Division Multiplexing) system is proposed for downlink in EUTRA. OFDM is a scheme which is used in IEEE802.11a that is a wireless system of 5 GHz-band and digital terrestrial broadcasting, and which provides simultaneous communications with tens to thousands of carriers allocated in minimum frequency-intervals that do not cause interference in theory. Generally, the carrier is referred to as a subcarrier in OFDM. Then, digital modulation such as PSK, QAM or the like is performed on each subcarrier to perform communications.
FIG. 15 is a diagram showing a configuration example of a downlink radio frame assumed based on the proposal of 3GPP in EUTRA (see Non-patent Documents 1 to 3). As shown in FIG. 15, the downlink radio frame is comprised of a plurality of blocks each of which is a unit radio resource used in communications. There is the case that block is referred to as Chunk.
Further, the block is comprised of a plurality of sub-blocks, with the sub-block as a minimum unit being defined by a sub-channel as a frequency component corresponding to a single or plurality of subcarriers and a sub-slot as a time component corresponding to a single or plurality of OFDM symbols.
The slot is expressed in two dimensions of a block bandwidth on the frequency axis and a slot on the time axis. There is the case that this slot is referred to as TTI (Transmission Time Interval). For example, when it is assumed that the entire downlink band (downlink frequency bandwidth) Ball is 20 MHz, a block bandwidth Bch is 300 kHz, a subcarrier frequency bandwidth Bsc is 15 kHz, a single radio frame length is 10 ms, and that TTI is 0.5 ms, a single radio frame is comprised of sixty blocks on the frequency axis and twenty blocks on the time axis, i.e. 1200 blocks.
Further, one block contains twenty subcarriers, and when the OFDM symbol duration Ts is assumed to be 0.0625 ms, it is calculated that one block contains eight OFDM symbols. Accordingly, as shown in FIG. 16, one block can be expressed by configuration C(f,t) when the number of sub-channels is f and the number of sub-slots is t (in the above-mentioned example, when it is assumed that one sub-channel is one subcarrier, and that one sub-slot is one OFDM symbol, equations of 1≦f≦20 and 1≦t≦8 hold).
In the block are mapped:    (1) user data for use by a user;    (2) physical and layer 2 control messages (hereinafter, referred to as “shared control information”) included in Downlink Shared Control Signaling Channel (DSCSCH) storing a mobile station ID (UE identity), modulation scheme, error correcting scheme, information required for the processing of Hybrid Automatic Repeat reQuest (HARQ), and transmission parameters such as a data length and the like; and    (3) a known pilot signal used in propagation path estimation to demodulate control data and user data.
Further, at the beginning of the radio frame are mapped (1) a synchronization signal to acquire synchronization of the frame and (2) common control information to broadcast the structure of the entire frame.
The shared control information is described in Non-patent Document 2. In other words, Non-patent Document 2 defines as channels in the physical layer:    (1) Pilot channel (Pilot signal);    (2) Common control channel (common control information);    (3) Shared control signaling channel (shared control information);    (4) Shared data channel (user data);    (5) Multicast/Broadcast channel; and    (6) Downlink synchronization channel (synchronization signal.
A block (chunk) to transmit data to a terminal (user, mobile station) is basically comprised of a pilot channel (pilot signal), shared control signaling channel (shared control information) and shared data channel (user data).
The pilot channel (pilot signal) is used in power measurement in performing a cell search and handover, CQI measurement to perform adaptive modulation, and channel estimation to demodulate the shared control information and user data.
The shared control signaling channel (shared control information) includes control information required for demodulation of user data, such as a modulation scheme of the block (chunk), data length, position of data to the terminal in the block (chunk), Hybrid ARQ information, and the like, and further as control information for uplink from the terminal, information of power control, transmission timing control, timing at which the terminal has to transmit, modulation scheme, data length, ACK/NACK to the data transmitted from the terminal, and the like.
The shared data channel (user data) is user data of the above-mentioned block (chunk), and sometimes shared by a plurality of users.
To demodulate the user data, the information of the modulation scheme, data length and the like in the shared control information is indispensable, and to demodulate the shared control information, propagation path compensation is made using the pilot signal.
FIG. 17A is a diagram of a block extracted from FIG. 15, and FIG. 17B is a diagram of another extracted block of a structure with part of pilot signals arranged in the center of TTI as another configuration example that is similarly proposed. In both of FIGS. 17A and 17B, by allocating the shared control information to demodulate the user data at the beginning of the block, it is intended to ease demodulation of user data in the terminal. In other words, since the need is eliminated for processing of storing user data in a buffer until all the shared control information in the block is obtained and the like, it is possible to reduce the circuit scale, and further reduce the demodulation processing delay.
Moreover, the shared control information is data important to demodulate the user data, a noise-immunity fixed modulation scheme such as QPSK or the like is used for the information to prevent the occurrence of demodulation error, and the information is disposed near the pilot signal to enhance propagation path estimation accuracy.
Further, in EUTRA, the MIMO (Multi-Input Multi-Output) technique is used which is a technique of transmitting different signals from a plurality of transmission antennas, and receiving the signals with a plurality of reception antennas to separate the received signals. FIG. 18 is a concept diagram of a communication system using the MIMO technique. In the MIMO technique, a transmitter 100 has a plurality of (M) transmission antennas 101-1 to 101-M, a receiver 102 has a plurality of (N) reception antennas 103-1 to 103-N, and MIMO propagation paths are formed using the transmission antennas 101-1 to 101-M and reception antennas 103-1 to 103-N. Then, a plurality of different data signals is transmitted and received via a plurality of propagation paths by radio signals with the same frequency or in overlapping frequency bands.
Herein, it is assumed in FIG. 18 that a propagation path from the antenna 101-1 to antenna 103-1 is h11, a propagation path from the antenna 101-2 to antenna 103-1 is h21, a propagation path from the antenna 101-M to antenna 103-1 is hM1, and that, a propagation path from the antenna 101-M to antenna 103-N is hMN. When it is further assumed that a transmission signal from the antenna 101-1 is S1, a transmission signal from the antenna 101-2 is S2, a transmission signal from the antenna 101-M is SM, a received signal in the antenna 103-1 is R1, a received signal in the antenna 103-2 is R2, and that a received signal in the antenna 103-N is RN, following equation (1) holds.
                    [                  Eq          .                                          ⁢          1                ]                                                                      (                                                                      R                  1                                                                                                      R                  2                                                                                    ⋮                                                                                      R                  N                                                              )                =                              (                                                                                h                    11                                                                                        h                    21                                                                    …                                                                      h                                          M                      ⁢                                                                                          ⁢                      1                                                                                                                                        h                    12                                                                                        h                    22                                                                    …                                                                      h                                          M                      ⁢                                                                                          ⁢                      2                                                                                                                    ⋮                                                  ⋮                                                  ⋱                                                  ⋮                                                                                                  h                                          1                      ⁢                      N                                                                                                            h                                          2                      ⁢                      N                                                                                        …                                                                      h                    MN                                                                        )                    ·                      (                                                                                S                    1                                                                                                                    S                    2                                                                                                ⋮                                                                                                  S                    M                                                                        )                                              (        1        )            
To obtain each h with ease, for example, when it is assumed that M=2 and N=2, it is considered that sub-slots including pilot signals as shown in FIG. 17A are configured as shown in FIG. 19. In other words, it is controlled that on the sub-channel to transmit the pilot signal from the first transmission antenna, a signal is not transmitted from the second antenna. In the receiver, using only the pilot signals transmitted from the first transmission antenna among received pilot signals, it is possible to estimate propagation paths h11 and h12 by performing linear interpolation, averaging and the like among the pilots. Similarly, using only the pilot signals transmitted from the second transmission antenna among received pilot signals, it is possible to estimate propagation paths h21 and h22. Next, the receiver generates candidates S′1 and S′2 for the transmission signal, and obtains R′1 and R′2 from equation (2) as described below.
                    [                  Eq          .                                          ⁢          2                ]                                                                      (                                                                      R                  1                  ′                                                                                                      R                  2                  ′                                                              )                =                              (                                                                                h                    11                                                                                        h                    21                                                                                                                    h                    12                                                                                        h                    22                                                                        )                    ·                      (                                                                                S                    1                    ′                                                                                                                    S                    2                    ′                                                                        )                                              (        2        )            
Then, a difference is obtained between R′ obtained in the above-mentioned equation and received signal R, and S′ that minimizes the difference is output as a signal S to be desired. This method is called MLC(Maximum Likelihood Detection), and further, another reception method is considered such as QRM-MLD as shown in Non-patent Document 4 although descriptions thereof are omitted herein.
When configurations in one block for each antenna in using the MIMO technique are defined as C1(f,t), C2(f,t), . . . , CM(f,t), pilot signals are required for each antenna to use the MIMO technique. For example, when the number of transmission antennas is two (M=2), such a block structure has been proposed that as shown in FIG. 20, in a position in the configuration where a pilot signal is transmitted from the first antenna, a pilot signal is not transmitted from the other transmission antenna (second transmission antenna) (null is disposed), thereby enabling the receiver to receive the independent pilot signal for each antenna, and that the other shared control information and user data is transmitted concurrently from each antenna.
As described above, the MIMO technique is a technique applicable on a block basis, and it is possible to provide both a MIMO block and non-MIMO block in a frame of EUTRA.
Using the frame structure as described above, described next is transmission and reception assumed based on the proposal of 3GPP with reference to drawings. FIG. 21 is a block diagram showing a schematic configuration of a conventional transmitter, and FIGS. 22 and 23 are block diagrams showing schematic configurations of conventional receivers. In addition, in the following description, it is assumed that a single block in a single radio frame is assigned to a single user. However, without being limited thereto, one user may use a plurality of blocks, or one block may be shared by a plurality of users.
As shown in FIG. 21, for example, in the transmitter in a base station, transmission data (shared control information and user data) for each user subjected to modulation processing is input to mapping circuits 120-1 to 120-n of each block together with a pilot signal. Each of the mapping circuits 120-1 to 120-n is comprised of a selector 120a, splitter 120b, and memories 120c-1 to 120c-M, and to provide the block structure as shown in FIG. 17A, the transmission data of each user and the pilot signal is arranged on the memories (configuration of FIG. 16) via the selector 120a and splitter 120b. Herein, in the block using the MIMO technique, the pilot signal is allocated to the memory of each antenna from the selector 120a, and the shared control information and user data is output to the memory of each antenna from the splitter 120b. In the block without using the MIMO technique, the same pilot signal and transmission data is allocated for all the antennas.
Signals allocated onto the memories in each of the mapping circuits 120-1 to 120-n are sequentially output to F/T transform circuits 121-1 to 121-M for each antenna, starting with the beginning of the frame, and signals of the entire band are transformed by IFFT (Inverse Fast Fourier Transform) computation from signals in the frequency domain to signals in the time domain. The transformed signals are converted into analog signals in D/A conversion circuits 122-1 to 122-M, further converted into signals with frequencies to transmit in the frequency conversion circuits 123-1 to 123-M, and then, transmitted from a first transmission antenna 124-1 to Mth transmission antenna 124-M.
The terminal is beforehand notified of whether a block to the terminal is transmitted as a MIMO signal or a non-MIMO signal by advance information such as the common control information or the like. Based on the notified advance information, when the block to the terminal is a non-MIMO signal, the terminal demodulates the data by the following processing using the receiver as shown in FIG. 22. In other words, as shown in FIG. 22, the signal received in an antenna 130 is converted into a signal with an intermediate frequency in a frequency conversion circuit 131. The analog signal converted into the intermediate frequency is converted into a digital signal in an A/D conversion circuit 132, and output to a T/F transform circuit 133.
The signal input to the T/F transform circuit 133 is subjected to FFT (Fast Fourier Transform) computation, and the signal in the time domain is thereby transformed into the signal in the frequency domain. A propagation path estimating circuit 134 calculates a propagation path estimation value for each sub-channel from the change in phase•amplitude of the pilot signal that is a known signal, and outputs the value to a propagation path compensating circuit 135. Using the estimation value calculated in the propagation path estimating circuit 134, the propagation path compensating circuit 135 compensates the received signal transformed in the T/F transform circuit 133 to be a transmission signal prior to being changed by the propagation path. A data demodulation circuit 136 demodulates the data signal compensated in the propagation path compensating circuit 135.
Herein, as the method of calculating an estimation value in the propagation path estimating circuit 134, for example, methods as shown in FIG. 24A and FIG. 24B and the like can be adopted. The method as shown in FIG. 24A is to obtain an average of changes in phase•amplitude of a plurality of pilot signals, and use the obtained average value as the change in phase•amplitude of a sub-channel positioned between the pilot signals. The method as shown in FIG. 24B is to make linear interpolation of changes in phase•amplitude of a plurality of pilot signals, and use the obtained interpolation value as the change in phase•amplitude of a sub-channel positioned between the pilot signals.
Meanwhile, when the block to the terminal is a MIMO signal, the terminal demodulates the data by the following processing using the receiver of FIG. 23. In other words, as shown in FIG. 23, received signals received in a first reception antenna 140-1 to Nth reception antenna 140-N are converted into signals with the intermediate frequency in frequency conversion circuits 141-1 to 141-N, and then, converted into digital signals in A/D conversion circuits 142-1 to 142-N. The digital signals in the time domain converted in the A/D conversion circuits 142-1 to 142-N are transformed into signals in the frequency domain by FFT computation in T/F transform circuits 143-1 to 143-N, and output to an MLD (Maximum-Likelihood Detection) circuit 144. The MLD circuit 144 has a propagation path estimating circuit 145, metric circuit 146, and comparing circuit 147, performs propagation path estimation and demodulation processing of the data, and outputs reception data.    Non-patent Document 1: R1-050705 “Pilot Channel Structure in Evolved UTRA Downlink” 3GPP TSG RAN WG1 #42 on LTE London, UK, Aug. 29-Sep. 2, 2005    Non-patent Document 2: R1-050707 “Physical Channels and Multiplexing in Evolved UTRA Downlink” 3GPP TSG RAN WG1 #42 on LTE London, UK, Aug. 29-Sep. 2, 2005    Non-patent Document 3: R1-050852 “CQI-based Transmission Power Control for Control Channel in Evolved UTRA” 3GPP TSG RAN WG1 #42 on LTE London, UK, Aug. 29-Sep. 2, 2005    Non-patent Document 4: “MIMO (Multi Input Multi Output) Related Technique” Website of Japan Patent Office: http//www.jpo.go.jp/shiryou/s_sonota/hyoujun/gijutsu/mimo/mokuji.htm